Josephine Getsi in Peit constituency has become the first woman to win an open seat since Bougainville first held elections under its autonomy arrangements ten years ago.
Election officials in the PNG region have nearly completed the vote count after last month's election, with 30 of the 40 seats in the new Bougainville parliament declared.
There are three seats reserved for women in Bougainville but no final results have been released.
This year a total of 23 women contested the reserved seats and a record 11 were in the open seats.
Ms Getsi was competing against 11 men and did particularly well through the second preference votes re-allocated from unsuccessful candidates.
Momis set for re-election
In the president's race the incumbent John Momis had more than 32,000 of the 71,000 votes counted.
Sam Kauona remains in second place with just shy of 11,000 votes, Ishmael Toroama is third and Sam Akoitai fourth.
The three regional seats reserved for women and the three reserved for ex-combatants are among the ten still being counted.
The writs are to be returned by next Monday.